Abundant evidence obtained from experiments on muscle degeneration and limb regeneration indicates that motor nerve terminals release one or more "trophic substances," i.e., materials that are essential for the maintenance of normal structure and function of muscle. If identified, isolated and eventually, mass produced, these substance(s) could be used to prevent or cure muscular degeneration after axotomy and could be useful in the treatment of muscular dystrophies. However, in order to isolate these substances it is essential to develop a bioassay. The bioassay proposed in this application is based on the fact that muscular degeneration after axotomy is associated with the appearance of tetrodotoxin (TTX) insensitive Action Potentials (AP). Neuromuscular preparations in organ culture display TTX insensitive AP shortly after denervation. In our bioassay, a large number of such cultures will be periodically stimulated under TTX and the responses will be recorded automatically every hour in order to determine the effects of brain and nerve extracts on the delay in appearance of TTX insensitive A.P.'s. The nerve trophic substances should: (1) Prevent the appearance of TTX insensitive A.P.'s; (2) Maintain the normal A.P.'s; (3) Increase the electrophysiological survival of the cultures; and (4) Maintain the normal structure of the neuromuscular junction. Brain and/or nerve extracts having tropic effects will be subfractionated in an attempt to purify the material.